In industrial automation engineering installations and machinery, hazardous conditions must be reliably identified and the controlled installation or machinery must be rendered secure in such an event. According to the state of the art, dedicated recording, cabling and evaluation systems are mostly used for the transmission of security-related signals of this type.
The use of dedicated recording, wiring and evaluation systems entails in particular high cabling cost, with the inherent risk of incorrect wiring. Efforts are therefore also made to transmit security-related signals via a bus system of this type. However, the security and reliability of the data transfer must not be adversely affected by a bus system of this type.
The security-related signals can be transmitted via a separate, error-protected bus system. However, this runs counter to the general tendency to minimize the wiring outlay.
DE 43 12 305 A1 discloses a method for transferring data between an error-protected stored-program control and a number of input/output units via a bus control unit connected to the stored-program control and a serial bus system. The bus control unit transfers messages to the input/output units connected to the bus system. In this data transfer method, at least one of the input/output units is designed as a security unit. Messages transferred to the security unit are transferred redundantly and are checked to ascertain whether or not they are identical. The transferred messages are interpreted as correct only if they are identical.